The known vehicles, such as the autonomous carriage according to French Patent 2,172,687 and that cited in Revue Francaise de Mecanique 1987-4, move on wheels in the former and on metal belts in the latter. They are not self-steering and are guided by the tube walls. They can only overcome gentle slopes within the limit of their friction or adherence ensured by the weight of the apparatuses and an obstacle at the bottom of the tube prevents their advancing.
There is also known a climbing vehicle that is equipped with two driving wheels and four folding legs which ensure contact on the walls via spherical balls. With embodiments that are self-steering for avoiding certain obstacles. The spherical wheels make its progress impossible in tube portions which have significant roughnesses on the walls. Its traction capacity is limited to the friction or adherence of its two driving wheels, for six wheels in, contact and thus it cannot drag an umbilical line over a long distance.
The vehicle disclosed by French Patent 2,530,214 employs a module with two driving wheels and two wheels free in rotation to ensure adherence. It can steer itself, following the walls closely but, being close to the latter, it cannot avoid large obstacles such as sheaths. Furthermore, its adherence is limited to its two driving wheels and the vehicle is unstable. Actually, as soon as a wheel lost contact with the wall, the vehicle is unbalabnce. Also, its low adherence does not allow it to drag an umbilical line over distance.
The apparatus according to German Patent 26 40 055 is a manipulator employing assemblies of sets of three jacks to center itself, and not to ensure its adherence on the walls, since its wheels are not driving wheels. It is not a self-propelled vehicle, and it reaches its working position by gravity.
The vehicle according to European Patent Appliation Patent 0,181,558 moves by rolling along the bottom of tubes, ensuring its adherence by means of a set of wheels pushed by a jack. The position of its driving wheels does not allow it to steer itself in the tube in order to avoid obstacles. The arrangement of the mechanical elements forces the vehicle to maintain constant contact with all its wheels at the risk or rolling into a position which would cause it to lose its balance without permitting it to reestablish that balance.
The vehicle according to European Patent 0,085,504 moves by rolling along at the bottom of tubes, specifically pipelines. Held by three arms, it is substantially arranged concentric with the axis of the pipe by virtue of resilient arrangements. It is movable without being able to steer itself. The vehicle cannot circumvent a pipe connection or an obstacle.
The vehicle according to French Patent 2,638,813 is composed of a plurality of parts which can support each other in order to overcome an obstacle. It has sets of three telescopic screw jacks which allow it to be centered in the tube. However, its wheels are not directional wheels and, to overcome obstacles, it has to be carried by part of the other element. Its necessary robustness makes it heavy and it takes up a relatively significant space in the tube in relation to obstacles projecting into the tube. Its weight and the power necessary for operating the motors limit its operational range due to a voluminous umbilical line.
It is therefore an object of the present invention to eliminate these disadvantages, allowing the circumvention of obstacles and enabling the vehicle to travel long distances.